Eve, the Book of Genesis tells us, was formed from a rib from Adam, but the all-male vocal group Celtic Thunder followed Celtic Woman, whose ladies had been a roaring success for three years by the time the men got going, in 2007. The two groups in fact share a brain-parent, Irish producer Sharon Browne. But the men are hardly playing second fiddle. By 2008 they had already completed a US tour of 50 cities. They’ve since become a regular PBS attraction, and one former member, Damian McGinty, has gone on to star on “Glee.” This year they released their 10th CD, “Mythology”; on Tuesday, they’ll be performing live at the Orpheum Theatre in support of that album.

Speaking on a conference call with the group’s music director, David Munro, Browne explains that “Celtic Thunder was originally going to be called Celtic Man, and I actually had the concept for that one first. But I had been working with large numbers of male orchestras for over 20 years on stage, and I had a handful of boys at home, so frankly I was sick of men, for a while.” She adds that she would have gone for Celtic Man as a name, but her business partners objected, so the group became Celtic Thunder.

What is it about the popular appeal of the name “Celtic” anyway? Browne cites the most recent US census showing that “46 million people in America consider themselves Irish-American.” Munro says simply, “Salmon swimming upstream. Coming back to your roots.”

Munro acknowledges that, despite the name, Celtic Thunder is essentially an Irish singing group, but he points out that one of the six current members, George Donaldson, is Scottish. What’s behind it for him, he says, is “the Celtic love of storytelling. The oral tradition is very strong in Celtic cultures, and that’s something we push on stage all the time. When the boys stop telling stories in their performances, they’ve got something wrong.”

Browne makes it clear that Celtic Thunder isn’t just a bunch of Irish vocals, it’s an Irish show. “When I was casting, I wanted to find a group of men that spanned the range of ages, and stages, in a man’s life. The very first show ranged from 14 to 40. They were all different ages, obviously, and they were all very different personalities and different types of voices. And the material we were picking was to suit the character in terms of age, in terms of the stage they were in life as a man.”

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Celtic Thunder: “Mythology”

She says she passed up established artists in favor of new talent. She was looking for ability, but also for the character of the man and the charisma of the person. As for the music, she explains that “though the preference of fans is for the very traditional Irish songs and melodies, if we don’t give younger and new Irish songwriters and performers a chance, then we’re never going to have new traditional favorites.” The Celtic Thunder repertoire is nothing if not eclectic, ranging from Irish Gaelic numbers like “Dúlamán” and “Buachaill ón Éirne” and “Mo Ghile Mear” at one end to “Scarlet Ribbons” and “Over the Rainbow” and Garth Brooks’s “The Thunder Rolls” at the other. Munro says he’ll “take Celtic music and perhaps dress it up with a little more theater than normal.” He adds, “I’ll take inspiration from anywhere. Simon and Garfunkel weren’t Celtic, but there’s a Simon and Garfunkel song [“The Sound of Silence”] in the ‘Mythology’ show, so that works as well.”

On the albums, he says, the orchestras have been getting bigger and bigger; the one they used for the upcoming Christmas album, “Christmas Voices,” numbers 90. At the Orpheum, however, there’ll be space for only seven members of the Celtic Thunder Band, musicians he describes as “very accomplished at a variety of different instruments, so we try to spread them about as much as possible.”

As for “Mythology,” he says it’s “an umbrella title for what we’ve put on stage. There’s no through line, there’s no linear connection between one song and the other, except all the songs in their own way have a story to tell.”

Browne elaborates, “We wanted to get back to reinforcing who the characters in the show are. What they are in terms of men, what they represent to women. What kind of man they are. So we very carefully picked the songs to reflect the characters of each of the singers. David worked with various songwriters in Ireland getting original pieces for the show. And the harmonies in most of the ensemble numbers in ‘Mythology’ are very complex. It took a long time to get them right.”

Meanwhile, don’t despair of seeing Celtic Thunder live backed by more than a septet. “Christmas Voices” is due next month, and Browne says they’re “planning to do a Christmas symphony tour next year traveling around America and Canada visiting as a guest of various symphony orchestras. So we can actually get to play live with a real big orchestra.”

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